Prior methods for melt spinning of lead have already been published. Such lead fibers have already been presented for application to sound control and radiation shielding materials. Diameters of lead fibers made by any of the conventional melt spinning methods range from approx. 150 to 200 microns, whereas lead fibers having less than 60 microns in the diameter are not yet been commercially available.
This is because, when fine lead fibers are extruded through a very small hole, either dripping or clogging of the hole occurs within a very short time, or the output may sharply decrease, and as a result, such very fine lead fibers cannot stably be spun. This problem is particularly noticeable in the process of spinning high-purity lead, for example, more than 99.9% of the purity.
A preceding invention under the patent application publication TOKUKOSHO No. 49-16168, disclosed methods for eliminating such a defect in spinning lead. Said methods prevents spinneret holes from clogging by adding alloy elements so that the spinning of lead can be improved.
Nevertheless, said prior art needs addition of a large amount of a metal element; for example, 0.1 to 40% (by weight) of tin must be added, thus eventually resulting in lowered lead contents in the made-up fiber.
It is vitally important to inhibit generating even the slightest amount of characteristic X-rays when such a material comprising lead fibers is applied to the radiation shielding. In addition, since the higher the lead content in the fiber, the higher the radiation shielding effect, it is not desirable to use such lead fibers containing much metal element for radiation shielding.